1. Technical Field
This application relates to a method of removing oil from a mixture of tool steel swarf granular material and oil.
2. Background Information
This application relates to the process conditions in utilizing supercritical carbon dioxide (SCCO2) for substantial removal of residual cutting fluids, either oils and/or water, and at least partial removal of other contaminants from industrial grindings of tool steels that may be contaminated with aqueous and/or oil-based residual contaminates. The contaminant liquid can be recycled for reuse, and the solids can be recycled or remelted in the smelting process for reuse. If the contaminants are not removed, they present an environmental hazard when they are land filled or incinerated.
Supercritical carbon dioxide is carbon dioxide that is at a temperature and a pressure greater than Tr=1 and Pr=1. (Tr is T/Tc where T is the present temperature of the supercritical carbon dioxide and Tc is the critical temperature. Pr is P/Pc where P is the present pressure of the supercritical carbon dioxide and Pc is the critical pressure.) Tc, the critical temperature for carbon dioxide (CO2), is 31.1 degrees Celsius (° C.), or 304.1 degrees Kelvin (K), and Pc is 73 atmospheres (atm) or about 1073 pounds per square inch (PSI).
In more general terms, supercritical carbon dioxide refers to carbon dioxide that is in a fluid state while also being at or above both its critical temperature and pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP) or as a solid called dry ice when frozen. If the temperature and pressure are both increased from standard temperature and pressure to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid. More specifically, it behaves as a supercritical fluid above its critical temperature (31.1° C.) and critical pressure (73 atm), expanding to fill its container like a gas but with a density like that of a liquid. The supercritical fluid region of the phase diagram is defined as a temperature above the critical temperature (31.1° C.) to a pressure above the critical pressure (73.8 bar or 1070 PSI).